The present invention relates generally to semiconductor devices and, more particularly, to a concentrated electroless solution for selective deposition of cobalt and cobalt-based alloys onto a copper surface.
In ultra-large-scale integration (ULSI) microelectronic devices, copper (Cu) has almost completely replaced aluminum (Al) in the fabrication of interconnects. Those skilled in the art are familiar with the advantages of using copper instead of aluminum; however, there are problems associated with the use of copper. These problems include corrosion, weak adhesion, high chemical reactivity, and diffusion of copper into silicon (Si). One of the approaches used to overcome the electromigration or corrosion problems associated with copper is to form a capping/barrier layer by electroless deposition.
U.S. Pat. No. 6,902,605 B2 to Kolics et al. discloses an electroless solution for deposition of a cobalt (Co)-tungsten (W)-phosphorous (P)-boron (B) film onto a copper surface to form a capping/barrier layer. This solution has shown potential when used to form a capping/barrier layer on silicon wafers that use silicon oxide as a dielectric to insulate the copper interconnections from one another.
As the density of ULSI devices has increased, manufacturers have started to use a much wider variety of materials in ULSI fabrication. For example, different manufacturers might use completely different chemicals at the same stages of device fabrication. Further, different manufacturers might use different types of dielectric materials to insulate the copper interconnections from one another. As a result of these differences, an electroless chemistry that works in the fabrication of one device might not be useful in the fabrication of another device.
Silicon carbonitride-based dielectrics have shown promise in the fabrication of increasingly dense ULSI devices. When known electroless solutions (e.g., the solution disclosed by Kolics et al.) have been used to deposit a cobalt-based capping/barrier layer onto copper interconnections having a silicon carbonitride-based dielectric, cobalt particles have been deposited without selectivity on both the copper and the dielectric. This is highly undesirable because it causes short circuits in the electronic device.
Thus, in view of the foregoing, a need exists for an electroless solution for the deposition of cobalt-based alloys onto a copper surface that can be used in a wide range of conditions and with a wide range of dielectric materials, including silicon carbonitride-based dielectric materials.